As the performance and features of imaging apparatuses such as digital still cameras, digital video cameras, and the like have grown more sophisticated in recent years, there has been a growing demand for apparatuses equipped with zoom lenses with high resolution and high zoom ratio. Meanwhile, there has also been a great demand for downsizing imaging apparatuses such as digital still cameras, and, as a result, a corresponding demand for downsizing the imaging optical systems used in such cameras.
However, use of a zoom lens with a high zoom ratio is problematic in that it is likely to lead to degradation in image quality due to a camera shake, particularly when images are captured using higher power telephoto zoom. As one technique for moderating such degradation in image quality, a zoom lens is equipped with a stabilized mechanism which moves some lens groups constituting the zoom lens substantially perpendicularly to the optical axis thereof, so that an image on the image plane moves in the direction opposite to the direction to that which the image moves when the image on the image plane is moved as a result of vibration, such as that caused external factors such as camera shake.
Such a stabilizing mechanism comprises a movement and other moving components to move the lens groups perpendicularly to the optical axis, so that mounting the stabilized mechanism on the zoom lens may increase the size of the zoom lens.
Japanese Patent Laid-Open Publication No. 2004-252196 discloses a technique in which, in a so-called five-group zoom lens composed of five lens groups having positive, negative, positive, positive and positive refractive powers, which are sequentially arranged in that order from the object side, all the lens groups are independently moved along the optical axis to perform a zoom operation, and some lens groups constituting the third lens group is moved perpendicularly to the optical axis to prevent vibration.
In the art described in Japanese Patent Laid-Open Publication No. 2004-252196, the vibration-proof mechanism is provided on the third lens group moving along the optical axis integrally with an aperture diaphragm and a shutter adjusting the amount of light, and some lens groups composing the third lens group are moved perpendicularly to the optical axis to prevent vibration.
However, when the stabilizing mechanism is integrated with the third lens group along with the aperture diaphragm and the shutter, the components of each of the driving mechanisms must be arranged in close proximity to each other, which limits the space available for arranging these components. Avoiding interference between the components otherwise requires increasing the overall size of the lens unit.
Japanese Patent Laid-Open Publications Nos. 2002-107625, 2001-356270, Hei 11-344660, and Hei 10-9060 disclose aspects of a technique in which, in a five-group zoom lens composed of five lens-groups with positive, negative, positive, negative and positive refractive powers, which are sequentially arranged in that order from the object side, a part or all the lens groups are moved along the optical axis to perform zooming, and the third lens group or the fourth lens group, or some lens groups constituting the third lens group or the fourth lens group are moved perpendicularly to the optical axis to prevent vibration.
However, the zoom lens disclosed in Japanese Patent Laid-Open Publication No. 2002-107625 has a zoom ratio of about 3.5×. Neither this document, nor any of the others, discloses any technique for realizing a high zoom ratio of 10× or more.
In fact, the zoom lenses disclosed in Japanese Patent Laid-Open Publication No. 2001-356270, Japanese Patent Laid-Open Publication No. Hei 11-344660 and Japanese Patent Laid-Open Publication No. Hei 10-90601 are designed for low resolution application suitable for use with a video camera equipped with a solid-state imaging device of relatively small size, on the order of ⅓-inch to ⅙-inch, and with a smaller number of pixels, 0.35 million to 2 million pixels.
When the zoom lenses disclosed in the patent documents 3 to 5 are used in a digital camera equipped with a solid-state imaging device of relatively larger size, about 1/1.8-inch to 1/2.5-inch, and larger number of pixels, 4 million to 10 million, the total size of an imaging optical system must be increased according to the size of the solid-state imaging device to significantly increase the size of the system, which makes configuring a higher resolution system with this technology extremely problematic.